Multi-shot Launcher Comprising External Propellant

ABSTRACT

An underwater gun for firing stacked munitions includes external propellant bays. In some embodiments, after a first munition is launched from the barrel of the launcher, propellant in one of the external propellant bays is ignited. The gas that is generated upon ignition is routed to the bore of the barrel and expels water that is in the barrel. A munition is then immediately launched through the cleared barrel.

STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH

This invention was made with Government support under N00014-07-C-1103awarded by the U.S. Navy. The Government has certain rights in theinvention.

FIELD OF THE INVENTION

The present invention relates to munitions in general, and, moreparticularly, to weapons capable of launching multiple stackedprojectiles underwater.

BACKGROUND OF THE INVENTION

FIG. 1 depicts a partial, simplified view of barrel 102 of multi-shotgrenade launcher 100. In launcher 100, three grenades 104-1, 104-2, and104-3 are “stacked” one behind another in barrel 102. Grenade 104-1 isin position 1 (i.e., first to be launched), grenade 104-2 is in position2 and grenade 104-3 is in position 3 as the third grenade to belaunched. This “stacked” grenade launcher technology is available fromMetal Storm Inc. as the “3GL” 3-shot semi automatic modular grenadelauncher.

Attached to the aft end of each grenade is propulsion base 108. Thepropulsion base contains propellant that is used to launch the grenade.Pusher plate 106 is disposed between each grenade and its accompanyingpropulsion base. The pusher plate transmits the pressure generated bythe propellant to the grenade being launched. The purpose of the pusherplate is to distribute the force across the surface of the tail of themunition, thereby preventing damage.

The stacked-round approach discussed above is useful for other weaponsapplications as well. For example, it would be desirable to use stackedrounds to create a multi-shot gun that fires “supercavitating”projectiles underwater. Underwater guns are useful as anti-mine andanti-torpedo devices. Recently, autonomous underwater vehicles (AUVs)have been fitted with underwater guns for torpedo defense and underwater“hunter-killer” CONOPs.

A gun, especially one that fires a projectile at a high muzzle velocity,cannot be fired when water is in its barrel. If a firing where to incurin a water-filled barrel, a very high breach pressure would result asthe ignited propellant charge forces (or tries to force) the water outof the barrel. The likely result would be material failure of thebarrel. Moreover, even if the weapon doesn't catastrophically fail, themuzzle velocity of the projectile would be reduced, because of theadditional water mass that requires expulsion.

The prior art has proposed a number of solutions for waterproofing thebarrel of an underwater gun or for clearing water from its barrel beforefiring. But in the context of an underwater weapon having a highmuzzle-velocity, most prior-art solutions solve one problem—clearing thebarrel of water—only to create other problems.

U.S. Pat. No. 5,639,982 discloses a means for firing a fully automaticgun underwater using a blank barrel-clearance round. Blankbarrel-clearance rounds are alternated with live rounds of ammunition.To begin the process, a blank barrel-clearance round is first detonated.This creates gas and steam within the chamber that forms a bubble at themuzzle end of the barrel, thereby displacing water from the chamber. Alive round is then immediately fired. The process is repeated, wherebythe subsequent detonation of a blank barrel-clearance round displacesany water that has re-entered the barrel subsequent to the firing of thelive round.

The application of this solution to an underwater gun that firesstacked, “supercavitating” rounds is problematic. In particular, toachieve the high muzzle velocities required for a projectile tosupercavitate, tremendous pressure must be developed in the barrel uponpropellant ignition. The barrel-clearance rounds remaining in the barrelwill be exposed to an extreme static load—a load that is in factsufficient to damage barrel-clearance rounds—when a live round is fired.

SUMMARY OF THE INVENTION

The present invention provides a way to clear water, between firings,from an underwater multi-shot weapon that launches stacked projectilesat very high velocities.

The illustrative embodiment of the present invention is an underwatermulti-shot launcher that includes external propellant bays. The externalpropellant bays contain propellant that, when ignited, expels water fromthe barrel of the launcher. A small window of time is provided afterwater is expelled to launch a projectile.

In the illustrative embodiment, the launcher includes a water seal overthe muzzle to keep the barrel clear of water prior to launching thefirst projectile. In some embodiments, the water seal is a rupture disc.As the pressure rises within the barrel upon ignition of the propellantthat launches the first projectile, the rupture disc will eventuallyburst. After the rupture disc bursts and the first projectile islaunched, water is free to enter the barrel. To the extent thatprojectiles are not fired in rapid succession, water must be clearedfrom the barrel prior to firing each subsequent projectile.

To that end, and in accordance with the illustrative embodiment,external propellant bays are disposed outside of the launcher, but areplaced in fluidic communication with bore of the barrel through apressure relief system and several conduits/channels. Each externalpropellant bay includes propellant that, when ignited, generates a gas.The gas, which is conveyed to the bore of the barrel, raises thepressure in the bore to a level sufficient to expel water therefrom.This provides a brief window of time in which a projectile can belaunched.

In the illustrative embodiment, the pressure relief system comprises twopressure relief devices, at least one of which couples directly to theexternal propellant bay. The pressure relief device that is coupled tothe external propellant bay, which in the illustrative embodiment is arupture disc, relieves (e.g., bursts in the case of a rupture disc) whensubstantially all propellant is consumed such that a maximum amount ofgas is generated. When this pressure relief device relieves pressure,the gas enters a high-pressure conduit that leads to the second pressurerelief device. In the illustrative embodiment, the second pressurerelief device is fitted to an opening through the side of the barrel. Achannel leads from this opening to the bore of the barrel.

When exposed to the pressure in the high-pressure conduit, the secondpressure relief device relieves pressure, permitting the gas in thehigh-pressure conduit to flow (via the channel) to the bore of thelauncher. As a consequence, the pressure in the bore rapidly rises to alevel that is sufficient to expel water. In the illustrative embodiment,the second pressure relief device is a rupture disc. During launch of aprojectile, the second pressure-relief device holds pressure and therebyprevents propellant gas (that is generated during launch of aprojectile) from entering the high pressure conduit and it also preventswater that enters bore (after the launch of a projectile) from enteringthe high pressure conduit.

In some embodiments, the invention comprises a launcher for launchingstacked munitions under water, wherein the launcher comprises:

-   -   a barrel having a bore, wherein the bore is dimensioned to        contain at least a first munition in a first position for        launch, a second munition in a second position for launch, and a        third munition in a third position for launch, and wherein the        munitions are arranged one behind another;    -   a first channel leading from the bore to a first opening through        the external surface of the barrel; and    -   a first external propellant bay that contains an amount of        propellant that is sufficient for clearing water from the bore        after the first munition is fired, wherein the first external        propellant bay is in fluidic communication with the first        opening and the bore through a first pressure relief system.

In some other embodiments, the invention comprises a launcher forlaunching stacked munitions under water, wherein the launcher comprises:

-   -   a barrel having a bore, wherein the bore is dimensioned to        contain at least three munitions that are arranged one behind        another; and    -   an external propellant bay that is fluidically coupled to the        bore, wherein the external propellant bay comprises:        -   (a) an amount of propellant sufficient for clearing water            from the bore;        -   (b) a chamber into which the propellant expands as a gas            when ignited; and        -   (c) a pressure relief system that is configured to permit            the gas to egress from the external propellant bay when            propellant contained therein is consumed.

In yet some additional embodiments, the invention comprises a method forlaunching stacked munitions under water, comprising:

-   -   launching a first munition from a bore of a barrel of a        launcher;    -   generating an amount of gas that is sufficient to clear the bore        of water after the first munition launches, wherein the gas is        generated in a bay that is external to the launcher;    -   exceeding a relief pressure of a pressure relief system that        controls a flow of the gas from the bay;    -   delivering the gas to the bore of the barrel, thereby clearing        the bore of water for a period of time; and    -   launching a second munition within the period of time.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a partial view of a multi-shot launcher in the prior art.

FIG. 2 depicts an embodiment of an underwater, multi-shot launcher inaccordance with the illustrative embodiment of the present invention.

FIG. 3 depicts a longitudinal cross-section through the multi-shotlauncher of FIG. 2.

FIG. 4 depicts a fragmentary view of the multi-shot launcher of FIG. 3,showing additional details of the external propellant bay.

FIG. 5 depicts a fire control system.

DETAILED DESCRIPTION

The terms appearing below are defined for use in this disclosure and theappended claims as follows:

-   -   “Operatively Coupled” means that a first object, which might be        remote from a second object, can have some effect on the second        object or have some effect on a third object through the second        object, etc. For example, consider a rigid linkage having a        first end and a second end. The first end attaches to a plate        and the second end abuts a wall. The linkage is capable of        transferring, to the wall, a force that is received at the        plate. The linkage and the plate can therefore be considered to        be operatively coupled for transmitting a force.        Operatively-coupled objects need not be in direct contact with        one another and, as appropriate, can be coupled through any        medium (e.g., semiconductor, air, vacuum, water, copper, optical        fiber, etc.). The coupling between operatively-coupled objects        can transmit, as appropriate for the nature of the coupling and        the objects, any type of force, signal, charge, electrical        current, optical energy, etc. Consequently, operatively-coupled        objects can be electrically-coupled, hydraulically-coupled,        magnetically-coupled, mechanically-coupled, optically-coupled,        pneumatically-coupled, thermally-coupled, fluidically-coupled,        etc.    -   “Fluidically Coupled” means that, with respect to two regions,        fluid (i.e., liquid, vapor, gas) can move between the two        regions or that a change in pressure in one region can affect        the pressure in the other region, etc.    -   “Projectile” means an object propelled by the exertion of a        force that ceases after launch.    -   “Munition” means an object that is propelled by the exertion of        a force that either ceases after launch or continues after        launch.

The illustrative embodiment of the invention is directed to the launchof stacked projectiles underwater from a multi-shot launcher. FIG. 2depicts a side view of multi-shot launcher 200 in accordance with theillustrative embodiment of the present invention. FIG. 3 depicts alongitudinal cross section of launcher 200.

Launcher 200 comprises barrel 201, which, in the illustrativeembodiment, is composed of multiple flanged segments. In theillustrative embodiment, barrel 201 comprises four segments: forwardsegment 204, intermediate segments 206A and 206B, and aft segment 206C.Aft segment 206C is sealed by breech portion 208. Forward segment 204 isattached to segment 206A and sealed by water seal 202. In theillustrative embodiment, segments 206A, 206B, and 206C are identical.

Each segment 204, 206A, 206B, and 206C has a central bore that alignswith a long axis of the segment. When these segments are attached as inFIGS. 2 and 3, these bores transversely align to define bore 305 of thebarrel.

Each segment 206A, 206B, and 206C includes a plurality of ignitionprimers 210-1, 210-2, and 210-3, respectively. In the illustrativeembodiment, there are three primers 210-1 (only two of which are visiblein FIG. 2). Each segment also includes at least one pressure transducer212-1, 212-2, and 212-3, respectively. Segments 206A and 206B alsoinclude, in the illustrative embodiment, respective rupture discs 214-1and 214-2. The ignition primers, pressure transducers, and rupture discsare discussed in further detail later in this specification with respectto FIGS. 3 and 5.

FIG. 3 depicts three projectiles 320-1, 320-2, and 320-3 disposed inbore 305 of barrel 201. Pusher plates 322 abut the tail each of theseprojectiles. The pusher plates are intended to distribute, across thetail of the projectile being fired, the static load that is generated(due to a rapid rise in pressure) when the propellant for the projectileis ignited. The pusher plates are not attached to the adjacentprojectile, but when a projectile is launched, the associated pusherplate is ejected from the launcher as well.

In some embodiments, a load-redirecting pusher plate, such as isdisclosed in co-pending application Ser. No. 12/571,966 (incorporated byreference herein), is used in conjunction with at least some of theprojectiles. The load-redirecting pusher plate, which is different thanthe conventional pusher plates depicted in FIG. 3, redirects to thebarrel the static load (due to propellant ignition) that would otherwisebe borne by the projectiles that remain in the barrel.

Associated with each projectile is propellant cartridge 324. Thecartridge is filled with a propellant, such as SHP831, available fromGeneral Dynamics—Ordnance and Tactical Systems. The propellant providesthe motive force for launching the projectile. In the illustrativeembodiment, propellant cartridges 324 have a cylindrical shape. Eachcartridge 324 is disposed aft of its associated projectile. In theillustrative embodiment, the cartridge fits in an annular cavity that iscreated between mating portions of adjacent segments of launcher 200.Propellant gas ports 325 place bore 305 of the barrel in fluidiccommunication with propellant cartridge 324.

During launch of a projectile, initiation primers (e.g., 210-1, etc.)ignite the propellant in one of the propellant cartridges 324. Gas,which is generated upon propellant ignition, is conducted by propellantgas ports 325 to bore 305. In the illustrative embodiment, threepropellant gas ports 325 are disposed in barrel at the axial positioncorresponding to the location of each propellant cartridge 324 (althoughonly one gas port 325 is depicted at each such location as a consequenceof the cross-sectional depiction). Pressure rapidly rises in the boreand serves as the motive force for launching the projectile. A pressurereading can be obtained via pressure transducer 212.

It is understood that, for the illustrative embodiment, a trio ofinitiation primers and a trio of propellant gas ports are located ateach axial position corresponding to the location of a propellantcartridge. In the illustrative embodiment, there is one propellantcartridge per each projectile within the launcher. In some otherembodiments, a greater or less number of initiation primers andpropellant gas ports can be used in conjunction with each propellantcartridge. Also, in some embodiments, two or more propellant cartridgesare used to launch each projectile.

Since launcher 200 is intended to fire projectiles at underwater and athigh speed (such as is required to create a supercavitating mode ofoperation), several adaptations are required to the launcher. Inparticular, the launcher must include an adaptation that ensures thatbore 305 is clear of water when a projectile is fired. To that end,water seal 202 is provided. In the illustrative embodiment, water seal202 comprises a rupture disc 303. Prior to the first firing of launcher200, rupture disc 303 seals the muzzle of the launcher, therebypreventing water from entering bore 305. As the pressure rises withinbore 305 upon ignition of the propellant for projectile 320-1, therupture disc 303 will eventually burst. Burst pressure is a function ofthe prevailing pressures within the bore upon ignition as well as theoperating depth of the launcher. Those skilled in the art will be ableto determine a suitable burst pressure for rupture disc 303.

Extreme pressures are generated upon propellant ignition. As such, thepressure within bore 305 persists above the external water pressure (attypical operating depth) for a brief period of time (e.g., 100millisecs, etc.) as a function of pressure. Water is therefore preventedfrom entering bore 305 for this brief period of time following launch ofa projectile. As a consequence, if launcher 200 is to be operated in amanner in which all projectiles in launcher 200 are fired in immediatesuccession, bore 305 will remain clear of water during the launch of allprojectiles. For this type of operation, only water seal 202 isrequired.

It is appreciated that a rupture disc is a single-use device. In thepresent context, once rupture disc 303 bursts and projectile 320A islaunched, water will be free to enter bore 305 when bore pressuresubsides. As a consequence, to the extent that projectiles might not befired in rapid succession, an adaptation is required to clear water fromthe barrel prior to firing each projectile (after the first projectileis fired).

To that end, and in accordance with the illustrative embodiment,launcher 200 comprises external propellant bay(s) 330-1 and 330-2,hereinafter collectively or generically referenced as “externalpropellant bay(s) 330.” Each external propellant bay 330 is disposedoutside of launcher 200, but is placed in fluidic communication withbore 305 via conduits and/or passages, as discussed later in furtherdetail. Each external propellant bay 330 includes propellant that, whenignited, generates a gas. The gas, which is conveyed to bore 305, raisesthe pressure in the bore to a level sufficient to expel water therefrom.This provides a brief window of time in which a projectile can belaunched. Further discussion of external propellant bay 330 is providedin conjunction with FIG. 4.

With continuing reference to FIG. 3, launcher 200 includes (n−1)external propellant bays, wherein “n” is the maximum number ofprojectiles that can be contained in the launcher for firing. The reasonfor using (n−1) bays 330 is that, for the illustrative embodiment, bore305 is initially sealed by water seal 202 and is therefore free ofwater. As a consequence, an external propellant bay is not required toclear water prior to launching the first projectile. For example, in theillustrative embodiment in which the capacity of launcher 200 is threeprojectiles, two external propellant bays 330 are included. Externalpropellant bay 330-1 is used to clear the bore of water prior to firingprojectile 320B and external propellant bay 330-2 is used to clear thebore before firing projectile 320C.

Operation of launcher 200 is controlled via fire control system 340. Insome embodiments, fire control system 340 incorporates one or moreprocessor(s), processor-accessible information storage, transceiver(s),appropriate drivers, and, in some cases, a power supply. In someembodiments, the fire control system can be attached to launcher 200. Inthe more typical situation in which launcher 200 is mounted on AUV,etc., the fire control system is located elsewhere on the AUV itself.

Fire control system 340 responds to a command to “launch” that typicallyoriginates from another weapons-related system (e.g., on board the AUVor other underwater vehicle). For example, the command can be issuedfrom detection/ranging/targeting systems that have acquired a target anddetermined that a projectile should be launched. Further description offire control system 340 is provided in conjunction with the discussionof FIG. 5.

FIG. 4 depicts further detail external propellant bay 330-1 and theregion in FIG. 3 demarcated by dashed lines and referenced as “A.” ThisFigure depicts the launcher after the first projectile—projectile320-1—has been launched. The associated pusher plate 322 has beenejected from bore 305 and propellant cartridge 324 is spent.

External propellant bay 330-1 includes, within housing 450, propellant452, expansion chamber 454, initiation primer 456, and gas outletpassage 458. In some embodiments, propellant 452 is smokelesspropellant, such as 20N29 propellant manufactured by Vihtavuori Oy ofFinland. Initiation primer 456 is an electric ignition unit, well knownin the art, for igniting propellant 452. Upon ignition, propellantexpands as a gas into expansion chamber 454. In some embodiments, 50grams of 20N29 propellant is used and expansion chamber 454 provides avolume of 50 cubic centimeters. In conjunction with the presentdisclosure, those skilled in the art will be able to select an amount ofpropellant for clearing the bore of water as a function of bore volume,operating depth, and like considerations.

External propellant bay 330-1 is placed in fluidic communication withbore 305 of the launcher through a pressure relief system, high pressureconduit 328, and channel 326 within the barrel. In the illustrativeembodiment, the pressure relief system comprises two rupture discs 214-1and 460. Rupture disc 460 couples to gas outlet passage 458. Rupturedisc 460 ensures that substantially all propellant 452 is consumed. Inother words, pressure builds in expansion chamber 454 as the propellantburns. To generate enough pressure to reach the burst pressure ofrupture disc 460, substantially all propellant must be consumed.

High-pressure conduit 328 associated with external propellant bay 330-1leads from rupture disc 460 to rupture disc 214-1. Rupture disc 214-1 isfitted to opening 440 in section 206A of the barrel. Opening 440 is oneterminus of channel 326. This channel leads through the barrelterminating, at its other end, at bore 305. Rupture disc 214 is designedto burst when exposed to the pressure within high-pressure conduit 328,as caused by propellant ignition in external propellant bay 330-1 (afterrupture disc 460 bursts). But it will not burst when exposed to thepressure in bore 305 during launch. Therefore, rupture disc 214-1prevents propellant gas that is generated during launch of projectile320-1 from entering high pressure conduit 328. It also prevents waterthat enters bore 305 after the launch of projectile 320-1 from enteringhigh pressure conduit 328.

The pressure within bore 305 at launch is greater than the pressure inthe bore during water expulsion. As a consequence, the operation of therupture disc 214-1 is not symmetric. That is, this rupture disc isdesigned for “one-way” operation in that it can withstand more pressureon one side (i.e., the “bore side”) than the other side (i.e., the“high-pressure conduit side”). In some alternative embodiments, aone-way valve is used in place of rupture disc 214-1. A one-way valve(e.g., typically a ball valve) rated for a pressure that exceeds themaximum pressure experienced in the bore will not release at anypressure experienced in the bore. It will release, however, at someminimum pressure in the high-pressure conduit.

Thus, external propellant bay 330-1 is placed in fluidic communicationwith the bore of the barrel via channel 326, high pressure conduit 328,and a pressure relief system. The same is true for external propellantbay 330-2, which is disposed aft of projectile 320-2 and is used toclear water from the bore after the launch of projectile 320-2.

Referring now to FIG. 5, fire control system 340 is suitably connected(e.g., wire, etc.) to each triad of initiation primers 210-1, 210-2, and210-3 and to the initiation primers 456 for external propellant bays330-1 and 330-2 to deliver a control signal thereto to ignite propellantat an appropriate time. Furthermore, fire control system 340 isappropriately connected to pressure transducers 212-1, 212-2, and 212-3for receiving signals therefrom indicative of the pressure at variouslocations within bore 305. Fire control system 340 also receivesinformation concerning current depth (or ambient pressure).

Fire control system 340 keeps track of which, if any, projectiles havebeen fired to determine if water expulsion is required and, if so, whichexternal propellant bay 330 is to be used. Having received a command to“launch,” and having determined that the next projectile to launch isprojectile 320-2, fire control system 340 sends a signal to initiationprimer 456 of bay 330-1. The initiation primer ignites propellant 452,which expands into chamber 454. Once sufficient pressure builds inchamber 454 (and gas outlet passage 458), rupture disc 460 bursts.Pressure then rises in high-pressure conduit 328, which causes rupturedisc 214-1 to rupture. The gas generated by propellant 452 thenpressurizes bore 305 and expels all water.

There is a brief window of time (from the time when the propellant inexternal propellant bay 330-1 is ignited) in which to launch projectile320-2. Pressure transducer 212-1 monitors pressure in bore 305 andtransmits pressure measurement data to fire control system 340. The datais used by algorithms running on fire-control system's processor(s) todetermine when to send a signal to initiation primer 210-2 to ignite thepropellant to launch projectile 320-2. In some other embodiments,launcher includes additional pressure transducers (i.e., in addition to212-1, 212-2, and 212-3) to obtain pressure readings within bore 305.

In a typical scenario, there is approximately a 100-millisecond windowfor projectile launch from the time that bore 305 is clear of water. Itwill take a projectile about 10 milliseconds to egress from the barrelonce it begins to move. It will take about 70 millisecs for the ignitedpropellant to generate the requisite pressure to launch the projectile.As a consequence, in such a scenario, fire control system 340 can send asignal to initiation primer 210-2 as late as about 20 milliseconds afterwater has cleared the barrel (as determined by pressure readings withinthe bore, which are relayed to fire control system 340 from pressuretransducer 212-1).

In conjunction with the present disclosure, those skilled in the artwill be able to develop algorithms that are capable of determining whento ignite the propellant that launches a projectile.

It is to be understood that the disclosure teaches just one example ofthe illustrative embodiment and that many variations of the inventioncan easily be devised by those skilled in the art after reading thisdisclosure and that the scope of the present invention is to bedetermined by the following claims.

1. A launcher for launching stacked munitions under water, comprising: a barrel having a bore, wherein the bore is dimensioned to contain at least a first munition in a first position for launch, a second munition in a second position for launch, and a third munition in a third position for launch, and wherein the munitions are arranged one behind another; a first channel leading from the bore to a first opening through the external surface of the barrel; and a first external propellant bay that contains an amount of propellant that is sufficient for clearing water from the bore after the first munition is fired, wherein the first external propellant bay is in fluidic communication with the first opening and the bore through a first pressure relief system.
 2. The launcher of claim 1 further comprising a water seal that seals a muzzle of the bore prior to the launching the first munition.
 3. The launcher of claim 1 wherein the first channel is disposed aft of the first munition.
 4. The launcher of claim 1 further comprising a high pressure conduit, wherein the high pressure conduit fluidically couples the first external propellant bay to the first opening.
 5. The launcher of claim 1 wherein the first pressure relief system comprises a rupture disc, wherein the rupture disc is disposed at a gas outlet of the external propellant bay.
 6. The launcher of claim 4 wherein the first pressure relief system comprises a rupture disc, wherein the rupture disc is disposed between the first opening and the high pressure conduit.
 7. The launcher of claim 1 wherein the first pressure relief system comprises a rupture disc disposed at a gas outlet of the external propellant bay and a one-way pressure-relief device disposed between the first opening and the first rupture disc.
 8. The launcher of claim 3 further comprising: a second channel leading from the bore to a second opening through the external surface of the barrel; and a second external propellant bay that contains an amount of propellant that is sufficient for clearing water from the bore after the second munition is fired, wherein the second external propellant bay is in fluidic communication with the second opening and the bore through a second pressure relief system.
 9. The launcher of claim 8 wherein the second channel is disposed aft of the second munition.
 10. A launcher for launching stacked munitions under water, comprising: a barrel having a bore, wherein the bore is dimensioned to contain at least three munitions that are arranged one behind another; and an external propellant bay that is fluidically coupled to the bore, wherein the external propellant bay comprises: (a) an amount of propellant sufficient for clearing water from the bore; (b) a chamber into which the propellant expands as a gas when ignited; and (c) a pressure relief system that is configured to permit the gas to egress from the external propellant bay when propellant contained therein is consumed.
 11. The launcher of claim 10 further comprising a water seal that seals a muzzle of the bore prior to the launching the first munition.
 12. The launcher of claim 9 wherein the launcher comprises a number, p, of external propellant bays, wherein p=n−1, wherein n is the maximum number of munitions that can be contained in the launcher.
 13. A method for launching stacked munitions under water, comprising: launching a first munition from a bore of a barrel of a launcher; generating an amount of gas that is sufficient to clear the bore of water after the first munition launches, wherein the gas is generated in a bay that is external to the launcher; exceeding a relief pressure of a pressure relief system that controls a flow of the gas from the bay; delivering the gas to the bore of the barrel, thereby clearing the bore of water for a period of time; and launching a second munition within the period of time.
 14. The method of claim 13 wherein the operation of generating an amount of gas further comprises igniting a propellant that is stored in the bay.
 15. The method of claim 14 wherein the operation of generating an amount of gas further comprises enabling the gas that is generated when the propellant is ignited to expand into a chamber within the bay.
 16. The method of claim 13 wherein the operation of delivering the gas to the bore of the barrel further comprises conducting the gas through a high pressure conduit.
 17. The method of claim 16 wherein the operation of delivering the gas to the bore of the barrel further comprises rupturing a seal disposed between the high pressure conduit and the bore of the barrel. 